1. Field of the Invention
The present invention relates to a magnetic video reproducer. More specifically, it relates to a magnetic video reproducer applicable to a video tape recorder in which a cue track is provided on the magnetic tape separately from video tracks for recording cue signals.
2. Description of the Prior Art
In a conventional magnetic video reproducer, there is employed a method in which four pilot signals having frequencies different from each other are superposed on video signals to be recorded in a magnetic tape, thereby to control reading positions of a video head based on the pilot signals. Such a control method is well known in the art by Dutch patent application No. 7702815 filed on Mar. 16, 1977 in the name of Hendrick, entitled "Method of and apparatus for controlling positions of writing and reading heads". A further teaching of recording on magnetic tape a composite signal including both video signals and pilot signals is disclosed in U.S. Pat. No. 4,297,733, incorporated herein by reference.
FIG. 1 is illustrative of video tracks provided on a magnetic tape T slantingly along the longitudinal direction thereof and pilot signals recorded on the respective video tracks in superposition with video signals. Referring to FIG. 1, description is now made with respect to a method of controlling a video head in a conventional magnetic video reproducer.
In FIG. 1, the magnetic tape T travels in the direction shown by an arrow a, i.e., in the forward direction. On video tracks F.sub.1, F.sub.2, F.sub.3 and F.sub.4, there are recorded pilot signals of frequencies f.sub.1, f.sub.2, f.sub.3 and f.sub.4 respectively. The relation between the respective frequencies is represented as follows: EQU .vertline.f.sub.2 -f.sub.1 .vertline..perspectiveto..vertline.f.sub.3 -f.sub.4 .vertline.=f.sub.a EQU .vertline.f.sub.1 -f.sub.4 .vertline..perspectiveto..vertline.f.sub.2 -f.sub.3 .vertline.=f.sub.b
in which the relation f.sub.a .noteq.f.sub.b is satisfied. It is assumed here that a magnetic head 10 is now tracking the video track F.sub.1 on the magnetic tape T as shown in FIG. 1. The pilot signal component detected by the magnetic head 10 includes, in addition to the pilot signal of the frequency f.sub.1 superposed on the video track F.sub.1, the pilot signals superposed on the adjacent video tracks F.sub.2 and F.sub.4 by a side leading effect and crosstalk etc. The ratio of these pilot signals detected from the adjacent video tracks F.sub.2 and F.sub.4 is increased following an increase in displacement of the video track F.sub.1 tracked by the magnetic head 10 from the central position.
Consequently, the aforementioned absolute values .vertline.f.sub.2 -f.sub.1 .vertline. and .vertline.f.sub.4 -f.sub.1 .vertline. are voltage-converted, whereby the direction of the tracking displacement of the magnetic head 10 is detected thereby to detect the amount of the subject displacement from the difference components. The detected error components are subjected to feedback to a servo circuit (not shown) to control travelling of the magnetic tape T.
Such a magnetic video reproducer in which the reading positions of the video tracks are controlled in the aforementioned manner has rapidly come into wide use, accompanied by multi-functionalization. In this regard, there is awaited implementation of a magnetic video reproducer which can perform program search for a recording starting position reliably in simple structure, though, no satisfactory device has been developed in practice.